Sara Shepard 
Toxic 

High school seniors Aria, Emily, Spencer, and Hanna barely survived their most recent encounter with A. And it’s not over yet . . . The police don’t believe that the real A is still out there, but the girls know what – and who – they saw. If they don’t track down this final tormentor soon, A will silence them forever.This penultimate installment of the beloved series is full of juicy scandals, dark secrets, and shocking plot twists that will prepare readers for the jaw-dropping series conclusion in Pretty Little Liars No 16.